Apparatus for controlling the effects of backlash

ABSTRACT

This disclosure describes an apparatus for controlling the rate at which the backlash of a mechanism is taken up. A demand signal causing rapid acceleration or rapid deceleration is modified prior to its application to the drive portion of the mechanism in an electrical or mechanical modifying system. The demand signal is modified in such a manner that it reduces or eliminates backlash to thereby reduce or eliminate the damage or noise caused by backlash.

United States Patent I Joseph Colin Whitehouse Humberstone, Leicester,England Dec. 9, 1968 Jan. 26, l 971 The Rank Organisation LimitedLondon, England Continuation-impart of application Ser. No. 578,082,Sept. 8, 1966, now abandoned.

Inventor Appl. No. Filed Patented Assignee APPARATUS FOR CONTROLLING THEEFFECTS OF BACKLASH 11 Claims, 29 Drawing Figs.

vs. C! 307/264; 74/583, 307/237, 328/169, 328/172 Int. Cl H03k 5/01,605g 7/00 Field of Search 74/1 583, (Inquired); 328/69, 1, 127, 132,168, 169, 172; 307/237, 264

[56] References Cited UNlT ED STATES PATENTS 1,738,281 12/1929 Bucklenet al. 74/583 2,449,035 9/1948 Coffin, Jr. et al. 328/l65X 3,030,0544/1962 Lee et al. 328/127X 3,219,936 11/1965 Eksten et a1. 328/1XPrimary Examiner- Donald D. Forrer Assistant Examiner-John ZazworskyAttorney Griffin, Branigan and Kindness ABSTRACT: This disclosuredescribes an apparatus for controlling the rate at which the backlash ofa mechanism is taken up. A demand signal causing rapid acceleration orrapid deceleration is modified prior to its application to the driveportion of the mechanism in an electrical or mechanical modifyingsystem. The demand signal is modified in such a manner .that it reducesor eliminates backlash to thereby reduce or eliminate the damage ornoise caused by backlash.

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APPARATUS FOR CONTROLLING THE EFFECTS OF BACKLASI-I BACKGROUND OF THEINVENTION rate at which the backlash of a mechanism is taken up. Whenmechanisms which exhibit backlash are subject to rapid accelerations ordecelerations, noise results. In addition, the pos sibility of damageexists due to the large impact forces which are created. For example,when a load driven through a mechanical gear arrangement from a powersource requires more (orless) power, backlash effects occur. Similarly,when a servo control system requires more (or less) electrical power,backlash effects occur. The amount of backlash effect involved isrelated to the amount of power increase (or decrease) applied and thetype of system involved, (i.e., mechanical gears, electrical servo,etc.).

There are two primary factors that contribute to backlash effects. Thefirst factor is the application of the power as a step function, (i.e.,power changes are rapidly applied). The second factor is the lost motionbetween the time of application of a power increase (or decrease) to thedrive means and the application of power by the drive means to the load.This lost motion period of time results in a shock when the drive meansengages the load. This shock creates backlash resulting in undesirablenoise and possible damage to the overall system.

Therefore, it is an object of this invention to provide an apparatus forreducing or eliminating the undesirable effect of backlash.

It is also an object of this invention to provide an apparatus forcontrolling backlash by modifying demanded power changes so thatbacklash is reduced or eliminated.

It is a still further object of this invention to provide an ap paratusfor controlling the application of power to a mechanism so that theshock which occurs when a drive means engages a load is reduced oreliminated.

SUMMARY OF THE INVENTION According to the present invention, anapparatus for use with mechanisms which employ drive and driven members(loads) that are subject to backlash effects is provided. The apparatusbasically comprises a means for modifying the input signal to the drivemember in a predetermined manner for a predetermined period of time sothat the relative velocity of the drive and driven member is small atthe instant of engagement. Thereafter, the full effect of the drivesignal (input signal) is restored to its unmodified form. That is, afterthe predetermined period of time has elapsed, the drive signal isallowed to reach its unmodified level.

While the invention may be used with various mechanisms that arecontrolled by electrical, mechanical, hydraulic, and other signals, thefollowing description refers in particular to the use of the inventionwith a speed control closed loop system that has a high inertia load andis controlled by a signal voltage through an amplifying device. Clearly,this system is such that backlash effects are severe. Following thedescription of the various arrangements for such a system, a particularexample of a speed controlled servooperating a zoom lens is described.In conclusion, various hydromechanical embodiments of the invention aredescribed.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred embodiments of theinvention will now be particularly described with reference to theaccompanying drawings wherein:

FIG. 1 is a pictorial diagram of a mechanical demand source coupled toan actuator through a backlash effect control;

FIG. 2 is an alternative pictorial diagram of a demand signal sourcecoupled to an actuator through a backlash effect control;

FIG. 3 is a pictorial diagram of a demand signal source coupled througha backlash effect control to an actuator that controls the movement of azoom lens mechanism;

FIG. 4 is a pictorial diagram of a drive and a load at rest; FIG. 5a isa velocity versus time diagram of the drive of FIG. 4 when a step inputis applied to said drive;

FIG. 5b is a velocity versus distance or phase plane diagram of thedrive load system of FIG. 4 when a step input is applied to drive;

FIG. 50 is a phase plane diagram of a drive-load system of FIG. 4 whenthe drive signal is modified;

FIG. 5d is a velocity versus time diagram illustrating the velocity thatmust be applied to the drive of FIG. 4 to result in the phase planediagram illustratedin FIG. 5c,

FIG. 6 is a pictorial diagram of the drive and the load under constantvelocity just prior to deceleration;

FIG. 7 is a velocity versus time diagram of the drive-load system ofFIG. 6 when a sudden deceleration is applied;

FIG. 8 is a phase plane diagram of the drive-load system of FIG. 6 for asudden deceleration;

FIG. 9 is a phase plane diagram of thedrive-load system of FIG. 6wherein the deceleration is modified;

FIG. 10 is a velocity versus time diagram for a modified decelerationresulting in a phase plane diagram of FIG. 9;

FIG. 11 is an optimum or ideal velocity or voltage versus time diagramincluding an acceleration backlash area; FIG. 11b is an optimum or idealvelocity voltage versus time diagram including a deceleration backlasharea;

FIG. is a phase plane diagram for either an 110 or an llb type ofbacklash;

FIG. 11d is an actual as opposed to an optimum (11b) diagram of voltageor velocity versus time for deceleration backlash;

FIG. 12 is a block diagram illustrating the overall concept of theinvention;

FIG. 13 is a schematic diagram illustrating one embodiment of theinvention;

FIG. 14 is a pictorial diagram illustrating the incoming demand signalfor the embodiment of the invention illustrated in FIG. 13;

FIG. 15 is a pictorial diagram of the modified demand signal generatedat the output of the embodiment of the invention illustrated in FIG. 13;

FIG. 16 is a pictorial diagram of a decelerating demand signal suitablefor application to the embodiment of the invention illustrated in FIG.13;

FIG. 17 is a phase plane diagram illustrating the modified output signalfor an embodiment of the invention of the type illustrated in FIG. 18;

FIG. 18 is a schematic diagram of an alternative embodiment of theinvention;

FIG. 19 is a schematic diagram of a still further embodiment of theinvention;

FIG. 20 is a schematic diagram of an embodiment of the inventionsuitable for use in the servo control system of a zoom lens;

FIG. 21 is a diagram of a mechanical embodiment of the invention;

FIG. 22 is a diagram of an alternative mechanical embodiment of theinvention; and

FIG. 23 is phase plane diagram for the embodiment of the inventionillustrated in FIG. 22.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 illustratevarious environments wherein backlash occurs. Specifically, FIG. 1illustrates a system wherein a demand signal source 11 is coupled to anactuator 13 via a backlash effect control 15 of the type illustrated inFIGS. 21 and 22, and hereinafter described. The demand signal sourceincludes a manually operable handle 17 coupled via a horizontallymovable rod 19 to the mechanical backlash effect control 15. Thebacklash effect control 15 is coupled to the actuator 13 via ahorizontally movable connecting rod 21.

When the manually operable handle 17 is moved to the right or left asviewed in FIG. 1, the movement is applied to the actuator 13 via thebacklash effect control 15. The backlash effect control modifiesmechanical signal in accordance with the principles herein described.

FIG. 2 illustrates an alternative system wherein a demand signal source23 is connected to an actuator 25 via a backlash effect control 27 ofthe type illustrated in FIGS. 21 and 22. The demand signal sourceincludes a rod 29 having a manually moveable handle 31. The rod 29 isattached at about its center to one end of a shaft 33 which is connectedto the backlash effect control 27. The backlash effect control 27 isconnected to the actuator via a further shaft 35. In addition amechanical feedback rod 37, connected to the mechanism to be actuated,is connected to the lower end of the rod 29. As the manually moveablehandle 31 is moved back and forth, in the direction illustrated in FIG.2, the thusly created mechanical signal is applied via the backlasheffect control 27 to the actuator 25.

FIG. 3 illustrates a system that utilizes an electronic backlash effectcontrol 39 of the type herein described. The electronic backlash effectcontrol 39 interconnects a demand signal source 41 to an actuator 43.The actuator 43 may be a servo motor having means for transferringrotary motion to lateral motion. The lateral motion is connected to azoom lens mechanism 45 via a rotatable coupling rod 47. In this manner,as the shaft 49 of the actuator 43 moves back and forth, the zoom lenselement 45 moves back and forth inside of a lens barrel 53.

It will be appreciated from viewing FIGS. 1-3, that the inventive systemincludes means for modifying a demand signal by a backlash effectcontrol. The backlash effect control, as hereinafter described, iseither mechanical or electrical and modifies the demand signal in such amanner that the effect of actuator backlash is reduced or entirelyeliminated.

Prior to describing an actual embodiment of the invention, theconditions existing when acceleration is taking place will be firstconsidered. FIGS. 4 and 5a thru 5d illustrate functionally anddiagrammatically certain of these conditions.

FIG. 1 illustrates a drive, D, adapted to drive a load. X represents thedistance that the drive moves through prior to engaging the load whenthe drive and the load initially are at rest. Hence, the drive could bethe shaft of a motor and the load could be a zoom lens, for example. Xthen represents lost motion distance between the shaft and the lensthrough a gear coupling means.

Assuming the drive and the load to be stationary, as illustrated in FIG.4, before the time (t=O) of engagement between the drive and the load,then for normal operation, the application of an input signal to thedrive produces a step input of velocity to the drive D as illustrated inFIG. a. The phase plane diagram of X distance between drive and load)and (velocity of approach between drive and load) is as shown in FIG.5b. It will be appreciated that, under these conditions, the drive movesto the right (as viewed in FIG. 5a) at a constant speed and strikes theload at a velocity V thereby producing noise and possible damage.

The apparatus of the invention prevents the foregoing situation bymodifying the signal applied to the drive in such a way so as to producea very small value of =V (velocity at time of striking) when thedisplacement, X, is small. The resultant phase plane diagram isillustrated in FIG. 50. It will be appreciated that the value of thevelocity signal (V should be adjustable to suit the precise operatingconditions of the particular environment in which the invention is beingused. The velocity signal required at the drive D for the caseillustrated in FIG. 4 is shown in FIG. 5d with the time of operation ofthe modification of the input signal depending upon the distance to theregion AA (where backlash is removed) from the point of starting.

Referring now to FIGS. 6 to 10, the conditions existing when adeceleration, as opposed to an acceleration, signal is applied to thedrive means is considered. Assuming the drive D and the load to bemoving toward the left of FIG. 6 at velocity V a sudden deceleration tozero velocity of the drive D is produced by an input signal on the driveD of the type illustrated in FIG. 7. The resulting phase plane diagramis illus trated in FIG. 8, from which it can be seen that there is againan impact velocity equal to V (assuming the load continues moving at VTo obtain the desired result (i.e., a velocity of near zero afterdistance X has been traveled), the signal to the drive means must bemodified so that a phase plane diagram of the type illustrated in FIG. 9results. FIG. 10 illustrates how the signal to the drive means must bemodified to achieve this result.

Referring now to FIGS. 5d and 10, the shaded areas under these graphsrepresent a distance that is just greater than the backlash in themechanism involved. It is clear from the shape of the areas concerned,that the maximum acceptable value of V, and the amount of backlashgovern the time that the modifying device need be operative. FIGS. 11aand 11b show the optimum type of demand signal for acceleration anddeceleration, respectively, resulting in smaller application time and,hence, better frequency response than a less optimum type of demandsignal. The corresponding phase plane diagram for FIG. 11b isillustrated in FIG. 110. Several embodiments of the invention resultingin a nearly optimum modify demand signal are hereinafter described.

FIG. 12 illustrates, in block form, how the demand signal is modifiedprior to the application to the demand element. More specifically, fromFIG. 12 it can be seen that a demand signal which is to be applied to aparticular mechanism in response to a particular demand is fed through amodifying system to produce a modified input signal for the mechanism.Depending upon the type of demand signal, the modifying system can beelectrical, mechanical, hydrostatic, or pneumatic, for example. Themodifying system operates in accordance with the principles outlined inconnection with FIGS. 4-11. That is, the demand signal which is tooperate the mechanism, is modified in accordance with a predeterminedsignal modification prior to application to the mechanism. For example,when the demand signal is an electric voltage, an electric modifyingsystem is used. Alternatively, the demand signal could be a mechanicallygenerated demand signal, used in combination with a mechanically poweredactuator.

The least complex embodiment of the invention is illustrated in FIG. 18and comprises a two stage RC filter with ganged variable resistors. Thefilters are L-stage filters with the resistor being connected in seriesand the capacitor being connected in shunt. This embodiment of theinvention is con nected as illustrated in FIG. 18 so that the electricaldemand input is connected across one filter combination and the modifiedinput electrical signal to the mechanism is taken across the capacitorof the second filter. This embodiment modifies electrical signals forboth accelerating and decelerating demands. The action of the filter isthat of a double integrator and by the choice of a suitable timeconstant, a decelerating step input signal (FIG. 16) is modified to thatshown in FIG. 17 so that the velocity is reduced to prevent backlash. Itwill be understood that varying the settings of the variable resistors Rwill alter the time period over which the velocity reduction occurs. Asimilar diagram to that illustrated in FIG. 17 can be drawn for anaccelerating step input electrical signal. It will be appreciated bythose skilled in the art and others, that the FIG. 18 embodiment isrelatively slow acting, hence, it finds its greatest use when a largebacklash is involved.

In many applications the sluggishness resulting from a large delay isunacceptable. For such systems, the embodiment of the inventionillustrated in FIG. 13 and hereinafter described which results inconditions approximating more clearly those described in connection withFIGS. 11a and 11b can be used. In this embodiment, the accelerating anddecelerating demand signals are modified separately by different devicesfor convemence.

For a positive step input at terminal X, a positive signal istransmitted through a variable resistor R31 and a capacitor 13C to thebases of two transistors, Q1 and Q2. The emitters of Q1 and Q2 areconnected to ground. O1 is a PNP transistor and O2 is an NPN transistor.A resistor, R4], is connected between the input terminal X and theoutput terminal Y. A second variable resistor R11, is connected betweenthe collector of Q1 and terminal Y and a third variable resistor, R21,is connected between the collector of Q2 and terminal Y. If the inputsignal has a significant magnitude, for example more than one-half volt,O2 is switched on (saturated) and the modified signal voltage applied tooutput terminal Y is the bottoming voltage of Q2. PNP transistor Q1,remains off because the positive input at its base is ineffective toturn it on.

Transistor Q2 remains saturated on until the voltage on its base becomesless than approximately one-half volt (in this example) or,. accordingto the V of the transistor used, becomes less that the saturating basevoltage. This occurs when capacitor 13C is charged up to the demandsignal voltage level through variable resistor, R31. The time constantof this charging period is governed by the adjustment of the variableresistor R31. When transistor Q2 is saturated, the magnitude of themodified signal voltage produced is adjusted by varying the thirdvariable resistor R21.

For a significant negative signal, transistor O2 is switched off andtransistor Q1 is switched on. The demand signal and the modified demandsignal for the embodiment shown in FIG. 13 are illustrated in FIGS. 14and 15, respectively. The shaded portion in FIG. 15 is related to thedistance traveled if the drive is a speed controlled device.Consequently, from the foregoing discussion, it will be appreciated thatthis area should represent a distance slightly greater than the backlashof the system. It can be seen that the modified demand signalillustrated in FIG. 15 more clearly approaches the optimum demand signalillustrated in FIG. 11a than a modified signal which results from theuse of the embodiment of the invention illustrated in FIG. 18.

For decelerating demands to zero, the sluggishness introduced by thefilters contained in the embodiment of the invention illustrated in FIG.18 is largely overcome by using a smaller capacitor charged up toavoltage V while the demand is on and applying this voltage to a systemhaving a time delay 8 after the demand ceases. The voltage V, isobtained by the linear amplification of the demand voltage and istherefore proportional to and, in general, larger than the V voltage.The resulting signal is illustrated in FIG. 11d. It can be seen thatthis signal approximates the 11b signal provided area B is smallcompared with area A. The backlash of this system is A+c-B. Thismodified RC only embodiment of the invention results in reducedapplication time of the modified signal. As the capacitance is nowsmaller than in the previous embodiment (FIG. 18) the sluggishness ofthe overall system is substantially reduced.

In the modified RC only embodiment, the capacitor is made ineffective inthe demand lead while the demand is on and is charged during this time.When the demand ceases, the capacitor is switched into the demand leadby the action of a relay or other suitable switch. Such an embodiment isillus trated in FIG. 19.

During the time the demand exists, the relay in FIG. 19 is in theposition illustrated and the capacitor 19C is charged up to a voltageequivalent to V and proportional to V The magnitude of V is determinedby the values of R20 and R and the resistance of a linear amplifier (notshown). The amplifier is connected to receive the demand signal. And,R30 and R20 form a voltage divider which applies this signal tocapacitor 19C. On relaxing the demand signal, the relay contacts switchpositions and the voltage previously applied to the capacitor becomesthe demand signal after a fixed time delay 8 governed by eitherelectrically slugging the relay coil or adjusting the relay mechanics.The voltage across the capacitor 19C then decays exponentially with atime constant depending upon the value of its discharge resistor R10 andthe parallel input impedance of the amplifier receiving the modifiedsignal (if one is used). Adjustment for different amounts of backlashare made by altering the values of V 8, and the time constant of thecapacitor decay either singly or together.

The electrical arrangement previously described can be used with anymechanism that is electrically energized. The arrangement can be used inconnection with simple motorized mechanisms, but its important uses arein connection with the servocontrol of guns, and in connection with zoomlenses.

FIG. 20 shows a circuit diagram of an arrangement for applying theinvention to a servo-controlled zoom lens and enables simple speedcontrol and position control. From observing FIG. 20, it will be seenthat the arrangement is essentially a combination of the embodiments ofthe invention described above and illustrated in FIGS. 13 and 19. Forposition demand control, a demand potentiometer DP, included in a demandposition servo, is variable to supply a position demand signal. That is,when the position of the demand potentiometer is changed, a demandsignal occurs. The position demand signal drops across a summingresistor SR in an amount determined by a signal originating at a resetposition potentiometer RP. The reset position potentiometer has its tapconnected to the load so as to sense the position of the load. Thesignal from RP is connected to the other end of SR via a pick offnetwork N which preferably includes a compensation capacitor as shown bythe dashed line. The signal from the summing point S serves to maintain,for a given position demand signal, a load at a substantially constantposition. The load being driven by a rate servomechanism or velodynefrom a terminal TD. During an interval between the initial applicationof a desired position demand signal by the demand potentiometer and theachievement final equilibrium, the voltage error to earth from thesumming point S is limited by a voltage limiting circuit VLT. Due to thebacklash present in the load, it is advantageous to control the signalat terminal TD in the manner indicated herein, thereby, preventing noiseand possible damage. That is, as hereinafter described, means of thetype previously described, are included to modify the demand signalduring its application to the load (zoom lens) connected to point TD soas to prevent backlash from occurring.

To the foregoing end, an arrangement A in accordance with thatillustrated in FIG. 13 is included so as to operate substantially asdescribed in connection with FIGS. 14 and 15 with respect to suddenchanges in the signal from the demand potentiometer DP. Conduction ofone of the transistors of the arrangement A is caused according to thepolarity of the sufficiently large new position demand signal relativeto the previous steady condition. When either of these transistors isswitched on for the period determined by the discharge time of thecapacitance of the arrangement A, its emitter-collector voltage issmall. Because the emitter-collector voltage is small and because thevariable resistance connected to its collector is small; the voltagefrom the summing point to earth is also small. Hence, a small signalexists at TD.

With the relay control contacts RC of arrangement B in the positionshown, the voltage at terminal TD constitutes a small demand input tothe rate servomechanism so that the speed of the load is small. After atime sufficient for backlash to be taken up, the transistor A switchesoff and the speed of the load is determined by the voltage limitingcircuit VLT until such time as the desired new position is reached andthe voltage at the summing point S is insufficient to actuate thevoltage limiting circuit VLT. Movement of the load then stops. Thevariable resistor VR affords a means for varying the time of applicationof the modified rate demand signal.

The remainder of the circuit illustrated in FIG. 20 comprises a circuitof the type shown in FIG. 19 for controlling the rate demand signal atterminal TD due to operation of a zoom control potentiometer ZR when therelay contacts RC are shifted from the position shown to their otherposition. Prior to this relay operation, which is preferably pushbuttoncontrolled, the voltage across' capacitor 20C is substantiallyproportional to the speed of the position servo because the voltageacross the resistor VR is substantially proportional to speed oftransverse of the moving contact of the reset potentiometer RP due todifferentiating capacitor-resistor elements (R1 and Cl) illustrated inFIG. 20. Thus, if such relay operation occurs at a time when the signalat the terminal TD is being adjusted for a changed position demandsignal, the voltage across the capacitor C is fed to the terminal TD andcauses the rate servo to come to rest in a manner tending to reduce therelative velocity between the drive and the driven members thereof,thereby reducing the unwanted effects due to backlash.

As with the arrangement of FIG. 19, a delay equal to the drop out timeof the relay combined with a relatively small capacitance 20C (comparedas before with the arrangement of FIG. 18) results in operationsubstantially as shown in FIG. 11d. It should be noted that, due to thenature of the drive and driven members generally the drop in thevelocity of the drive members in the interval '0 will, in practice, beexponential and the rise after the interval will also not beinstantaneous. During this time, the velocity of the driven member willalso be falling slightly in a substantially linear manner.

Mechanical, hydraulic, or pneumatic systems operating analogously to theabove described electrical systems may be used for appropriate type ofdemand signals, one such mechanical system is illustrated in FIG. 21.This system incorporates two mechanical filters connected in series eachcomprising an oil dashpot 100, 100' and a spring 101, 101, which are theanalogue of the electric filter illustrated in FIG. 18. The timeconstants of the filters can be changed by altering the viscosity of theoil 102, 102 in the dashpots or the rates of the springs.

Each dashpot 100, 100' has a plunger 103, 103 bored at 104, 104 foroperation in its oil chamber. The plunger shafts 105, 105 are sealed at106, 106 on each end of the respective oil chamber and protrude at 107,107 into a closed end 108, 108' of the respective dashpot body. Thespaces between the ends 108, 108' and the plunger parts 107, 107' arearranged so that the maximum plunger travel is, preferably, just greaterthan the backlash of the load driven from the shaft 109. A frictionloading 110, on the shaft 109 is also provided.

In operation, the full effect of the sudden change of a demand signalapplied to the shaft 105 is not transmitted to the shaft 109 untilmovement of the plunger shafts 105, 105 toward the ends 108, 108 hastaken place. As this is greater than the backlash in the load, thecharacteristics of this system will, as described above, be similar tothose for FIG. 18.

In order to obtain a mechanical device exhibiting the delaycharacteristics similar to those associated with FIGS. 11a and 11b, itis convenient to use a mechanism which itself has controlled backlash,such as a device of the type illustrated in FIG. 22. This arrangementcomprises a dashpot 111 filed with oil 112 with an input shaft 113having a plunger 114 protruding as illustrated in FIG. 22. The axialmovement of the plunger 114 within the dashpot 111 is limited by theposition of adjustable end stops 115 located at one end of the dashpot111. The force transferred to the output shaft 116 when the plunger 114is not at the end stops 115 is altered by moving the oil 112 in thedashpot 111.

Considering the device illustrated in FIG. 22, it will be appreciatedthat the application of a force to the input or demand shaft 113 forcesthe plunger 114 into the body of the dashpot 111 providing the frictionloading 117 on the output shaft 116 is just greater than the loadingbetween the demand shaft 113 and the dashpot case seals 118. Themovement of the plunger 114 due to the oil holes 119 exerts a viscousforce on the walls of the dashpot 111 proportional to the relativevelocity between the dashpot 111 and the plunger 114. Equilibrium occurswhen the sum of the friction forces (i.e., the forces between thedashpot 111 and the plunger 114 and between the output shaft 116 and thefrictional clutch or loading 117) equals the applied force. In thiscondition, the input shaft 113 moves at a constant speed. The frictionloading on the output shaft 116 is composed of two parts. one beingfriction and the other viscous. The friction controls the large velocitydifferentials between the input and output shafts of the device.

Application of a force to the input shaft 113 initially produces amodified velocity demand on the output shaft 116 which is much less thana demand velocity. This operation continues until the plunger 114transverses the backlash in the dashpot 111. At this point, the modifieddemand velocity becomes equal to the input demand velocity. Adjustmentof the dashpot 111 to suit different degrees of system backlash is madeby alternating the amount of travel in the dashpot 111 using theadjustable end stops 115. The speed differential between the input andoutput shafts 113 and 116 is varied by altering the viscosity of the oil1 12 in the dashpot 111.

The device illustrated in FIG. 22 is used for both accelerating anddecelerating demand signals, the resulting phase plane diagram in bothcases is illustrated in FIG. 23. If this mechanism is to suffer fairlylarge impact velocities between the plunger 114 and the end stops 115,it may be necessary to terminate the end stops with shock absorbent pads120, thus reducing the risk of noise and damage in the device itself. Itwill be appreciated that the backlash in the device is set to be onlyjust greater than that in the system wherein it is being used.

I claim:

1. Apparatus including a backlash effect control comprising:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating an electrical demand signal inresponse to a demand; and

a backlash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising: switch means having a pair of two position contacts,each pair including a common contact for controlling the passage ofcurrent in an electric circuit, said switch means connected to receivethe electrical demand signal generated by said demand signal source;

a resistor;

a first variable resistor, said resistor and said first variableresistor connected in series one end of said series connection adaptedto receive the electrical demand signal generated by said demand signalsource, the junction between said series connection being connected toone terminal of the first of said two position contacts, the other endof said series connection being connected to ground and to the otherterminal of said first of said two position contacts;

a capacitor, one end of said capacitor connected to the common contactof said first of said two position contacts; and

a second variable resistor, said second variable resistor beingconnected between the other side of said capacitor and ground, thejunction between said capacitor and said second variable resistor beingconnected to one terminal of the second of two position contacts, theother terminal of said second of said two position contacts beingconnected to said demand signal source and the common terminal of saidsecond of said two position contacts being connected to saidelectrically operated actuator.

2. Apparatus including a backlash effect control comprismg:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating an electrical demand signal inresponse to a demand; and,

a backlash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising:

a first resistor having one end connected to said demand signal sourceand the other end connected to said electrically operated actuator;

a first variable resistor;

a capacitor, said first variable resistor and said capacitor connectedin series with the other end of said first variable resistor beingconnected to said demand signal source;

an NPN transistor having its base connected to the other side of saidcapacitor and having its emitter connected to ground;

a PNP transistor having its base connected to the other side of saidcapacitor and its emitter connected to ground;

a second variable resistor having one end connected to the collector ofsaid NPN transistor and the other end connected to said electricallyoperated actuator; and

a third variable resistor having one end connected to the collector ofsaid PNP transistor and the other end connected to said electricallyoperated actuator.

3. Apparatus including a backlash effect control comprismg:

an electrically operated actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating an electrical demand signal inresponse to a demand; and

a backlash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash efiect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising:

a position indicating means connected to said electrically operatedactuator for indicating the position of said actuator;

a summing means connected to said demand signal source and to saidposition means for summing signals from said demand signal source andfrom said position means; and

signal modifying means connected to said summing means for modifying thesignal from said summing means and for applying said modified signal tosaid electrically operated actuator.

4. Apparatus including a backlash effect control as claimed in claim 3wherein said position means comprises a potentiometer connected across apositive and negative source of voltage and having its wiper armconnected to said actuator so that said wiper arm moves as said actuatoroutput moves and wherein said summing means comprises a resistivenetwork connected to said wiper arm and to said demand signal source.

5. Apparatus including a backlash effect control as claimed in claim 4wherein said modifying means comprises:

transistor means connected to said resistive network and to saidactuator for modifying said demand signal in a predetermined manner. 6.Apparatus including a backlash effect control as claimed in claim 5wherein said transistor means comprises: a first resistor having one endconnected to said resistive network and the other end connected to saidactuator;

a first variable resistor;

a capacitor, said first variable resistor and said capacitor connectedin series with the other end of said capacitor being connected to saidresistive network;

an NPN transistor having its base connected to the other side of saidfirst variable resistor and having its emitter connected to ground;

a PNP transistor having its base connected to the other side of saidfirst variable resistor and its emitter connected to ground;

a second variable resistor having one end connected to the collector ofsaid NPN transistor and the other end connected to said actuator; and,

a third variable resistor having one end connected to the collector ofsaid PNP transistor and the other end connected to said actuator.

7. Apparatus including a backlash effect control as claimed in claim 6comprising a voltage limiting means connected between said modifyingmeans and said actuator.

8. Apparatus including a backlash effect control as claimed in claim 7wherein said modifying means also includes:

switch means having a pair of two position contacts, each pair having acommon contact, for controlling the passage of current in an electriccircuit;

a first capacitor;

a first resistor;

a variable resistor, said first capacitor, said first resistor and saidvariable resistor connected in series, one end of said series connectionadapted to receive the sum signal from said resistive network, thejunction between said variable resistor and said first resistor beingconnected to one terminal of the first of said two position contacts,the other end of said variable resistor being connected to ground;

a second capacitor, one end of said second capacitor being connected tothe common contact of said first of said two position contacts; and

a second resistor, said second resistor being connected between theother end of said second capacitor and ground, the junction between saidsecond capacitor and said second resistor being connected to oneterminal of the second of said two position contacts, the other terminalof said second of said two position contacts being connected to saidvoltage limiting means and the common terminal of said second of saidtwo position contacts being connected to said actuator.

9. Apparatus including a backlash effect control comprisa mechanicallypowered actuator for moving a mechanism,

said actuator having backlash generating elements;

a demand signal source for generating a mechanical power demand signalin response to a demand;

a backlash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred.

10. Apparatus including a backlash effect control as claimed in claim 9wherein said backlash effect control comprises first and second dashpotsand first and second springs connected in series between said demandsignal source and said actuator, each of said dashpots comprising ahousing having a plunger mounted therein with oil located between saidplunger and said housing.

11. Apparatus including a backlash efiect control as claimed in claim 9wherein said backlash effect control comprises a dashpot, said dashpotincluding a housing connected by a shaft to said actuator and furtherincluding a plunger conn nected by a second shaft to said demand signalsource, said housing including oil located therein about said plunger sothat the demand signal applied by said plunger to said housing ismodified by the viscosity of said oil.

1. Apparatus including a backlash effect control comprising: anelectrically operated actuator for moving a mechanism, said actuatorhaving backlash generating elements; a demand signal source forgenerating an electrical demand signal in response to a demand; and abacklash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising: switch means having a pair of two position contacts,each pair including a common contact for controlling the passage ofcurrent in an electric circuit, said switch means connected to receivethe electrical demand signal generated by said demand signal source; aresistor; a first variable resistor, said resistor and said firstvariable resistor connected in series one end of said series connectionadapted to receive the electrical demand signal generated by said demandsignal source, the junction between said series connection beingconnected to one terminal of the first of said two position contacts,the other end of said series connection being connected to ground and tothe other terminal of said first of said two position contacts; acapacitor, one end of said capacitor connected to the common contact ofsaid first of said two position contacts; and a second variableresistor, said second variable resistor being connected between theother side of said capacitor and ground, the junction between saidcapacitor and said second variable resistor being connected to oneterminal of the second of two position contacts, the other terminal ofsaid second of said two position contacts being connected to said demandsignal source and the common terminal of said second of said twoposition contacts being connected to said electrically operatedactuator.
 2. Apparatus including a backlash effect control comprising:an electrically operated actuator for moving a mechanism, said actuatorhaving backlash generating elements; a demand signal source forgenerating an electrical demand signal in response to a demand; and, abacklash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising: a first resistor having one end connected to saiddemand signal source and the other end connected to said electricallyoperated actuator; a first variable resistor; a capacitor, said firstvariable resistor and said capacitor connected in series with the otherend of said first variable resistor being connected to said demandsignal source; an NPN transistor having its base connected to the otherside of said capacitor and having its emitter connected to ground; a PNPtransistor having its base connected to the other side of said capacitorand its emitter connected to ground; a second variable resistor havingone end connected to the collector of said NPN transistor and the otherend connected to said electrically operated actuator; and a thirdvariable resistor having one end connectEd to the collector of said PNPtransistor and the other end connected to said electrically operatedactuator.
 3. Apparatus including a backlash effect control comprising:an electrically operated actuator for moving a mechanism, said actuatorhaving backlash generating elements; a demand signal source forgenerating an electrical demand signal in response to a demand; and abacklash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred, said backlash effectcontrol comprising: a position indicating means connected to saidelectrically operated actuator for indicating the position of saidactuator; a summing means connected to said demand signal source and tosaid position means for summing signals from said demand signal sourceand from said position means; and signal modifying means connected tosaid summing means for modifying the signal from said summing means andfor applying said modified signal to said electrically operatedactuator.
 4. Apparatus including a backlash effect control as claimed inclaim 3 wherein said position means comprises a potentiometer connectedacross a positive and negative source of voltage and having its wiperarm connected to said actuator so that said wiper arm moves as saidactuator output moves and wherein said summing means comprises aresistive network connected to said wiper arm and to said demand signalsource.
 5. Apparatus including a backlash effect control as claimed inclaim 4 wherein said modifying means comprises: transistor meansconnected to said resistive network and to said actuator for modifyingsaid demand signal in a predetermined manner.
 6. Apparatus including abacklash effect control as claimed in claim 5 wherein said transistormeans comprises: a first resistor having one end connected to saidresistive network and the other end connected to said actuator; a firstvariable resistor; a capacitor, said first variable resistor and saidcapacitor connected in series with the other end of said capacitor beingconnected to said resistive network; an NPN transistor having its baseconnected to the other side of said first variable resistor and havingits emitter connected to ground; a PNP transistor having its baseconnected to the other side of said first variable resistor and itsemitter connected to ground; a second variable resistor having one endconnected to the collector of said NPN transistor and the other endconnected to said actuator; and, a third variable resistor having oneend connected to the collector of said PNP transistor and the other endconnected to said actuator.
 7. Apparatus including a backlash effectcontrol as claimed in claim 6 comprising a voltage limiting meansconnected between said modifying means and said actuator.
 8. Apparatusincluding a backlash effect control as claimed in claim 7 wherein saidmodifying means also includes: switch means having a pair of twoposition contacts, each pair having a common contact, for controllingthe passage of current in an electric circuit; a first capacitor; afirst resistor; a variable resistor, said first capacitor, said firstresistor and said variable resistor connected in series, one end of saidseries connection adapted to receive the sum signal from said resistivenetwork, the junction between said variable resistor and said firstresistor being connected to one terminal of the first of said twoposition contacts, the other end of said variable resistor beingconnected to grOund; a second capacitor, one end of said secondcapacitor being connected to the common contact of said first of saidtwo position contacts; and a second resistor, said second resistor beingconnected between the other end of said second capacitor and ground, thejunction between said second capacitor and said second resistor beingconnected to one terminal of the second of said two position contacts,the other terminal of said second of said two position contacts beingconnected to said voltage limiting means and the common terminal of saidsecond of said two position contacts being connected to said actuator.9. Apparatus including a backlash effect control comprising: amechanically powered actuator for moving a mechanism, said actuatorhaving backlash generating elements; a demand signal source forgenerating a mechanical power demand signal in response to a demand; abacklash effect control connected to said demand signal source toreceive said demand signal and connected to said actuator for applying amodified demand signal to said actuator, said backlash effect controlmodifying said demand signal for a predetermined period of time after ithas been generated in response to a demand so that a low relativevelocity occurs between the backlash generating elements of saidactuator upon impact, said modified demand signal changing to anunmodified level after said impact has occurred.
 10. Apparatus includinga backlash effect control as claimed in claim 9 wherein said backlasheffect control comprises first and second dashpots and first and secondsprings connected in series between said demand signal source and saidactuator, each of said dashpots comprising a housing having a plungermounted therein with oil located between said plunger and said housing.11. Apparatus including a backlash effect control as claimed in claim 9wherein said backlash effect control comprises a dashpot, said dashpotincluding a housing connected by a shaft to said actuator and furtherincluding a plunger connected by a second shaft to said demand signalsource, said housing including oil located therein about said plunger sothat the demand signal applied by said plunger to said housing ismodified by the viscosity of said oil.